ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 269 



Ternary Systems.* — E. Janecke deals with the theory of ternary 

 systems, in which the equilibrium diagram shows a ternary transition- 

 point. The lead-cadmium-mereury system is considered as an example, 

 and photomicrographs are given to illustrate the author's conclusions. 



Cementation by Gases.j — A. Portevin opens a general review of 

 this subject, by pointing out that in industrial cementation the part 

 played by solid carbon is probably quite insignificant, the cementation 

 being effected almost wholly by gaseous carbon compounds. The study 

 of the laws governing cementation by gases should therefore precede 

 the investigation of the much more complex mechanism of cementation 

 by solid materials. Gaseous cementation agents may all be regarded as 

 following one of the three types : (1) carbon monoxide ; (2) cyanogen ; 

 (3) the hydrocarbons. Each one of these, in presence of iron at a high 

 temperature, is capable of decomposing into carbon and another gas. 

 The laws governing the phenomena are the same in each case, and the 

 author proceeds to work out in some detail the theory of the system 

 CO - C0 2 - C, as a representative case. 



A full account is then given of the extensive experimental work on 

 cementation by gases carried out by Giolitti and his pupils.J 



Cementation of Steel. § — F. Giolitti and F. Carnevali record the 

 results of experiments on the cementation of two steels, containing 

 respectively 0'18 p.c. and 0*94 p.c. carbon, at different temperatures, 

 the cementation media being ethylene, methane, carbon-monoxide, and 

 other gases. 



F. Giolitti and G. Tavanti || describe a method of cementation by 

 means of a mixture of carbon-monoxide and dioxide in equilibrium with 

 carbon at the cementation temperature. By this method the sharp 

 transition from a region of high-carbon content to a region of low-carbon 

 content is avoided. 



Cementation in a Vacuum. % — F. Weyl summarizes previous work 

 on cementation, and describes the experiments by which he has demon- 

 strated the possibility of the cementation of iron by pure carbon. Small 

 cubes of iron, prepared in an electric furnace, and containing ' 09 p.c. 

 carbon, ■ 3 p.c. manganese, were heated in a high vacuum at tempera- 

 tures between 750° C. and 1050° C, in contact with one of the following 

 varieties of carbon : sugar charcoal, Ceylon graphite, kish, and diamond 

 powder. These materials had been previously carefully purified and 

 heated for some time in a vacuum. Microscopical examination of the 

 specimens showed that cementation had occurred when a sufficiently 

 high temperature had been attained, but the smallness of the amount of 



* Zeitschr. Phys. Chem., lxxiii. (1910) pp. 328-42 (24 figs.). 

 t Rev. Metallurgie, vii. (1910) pp. 859-85 (23 figs.). 

 % See this Journal, 1909, 1910, 1911. 



§ Atti R. Accad. Sci. Torino, xlv. (1910) pp. 376-87, through Joura. Chem. Soc, 

 xcviii. (1910) p. 616. 



ij Tom. cit., pp. 539-63, through Journ. Chem. Soc, xcviii. (1910) pp. 780-1. 

 1 Metallurgie, vii. (1910) pp. 440-56 (39 figs.). 



April 19th, 1911 T 



